Electric heating unit



Jan. 23,. 1940. w. o. TWOMBLY 3,

ELECTRIC HEATING UNIT Filed July 1, 1936 L Tmi' I [I s i' l 2 e 3 f 2 \L I w v m 71 A I Snwcntot Patented Jan. 23, 1940 UNITED STATES PATENT OFFICE ELECTRIC HEATING UNIT Application July 1, 1936, Serial No. 88,368

1 Claim.

This invention relates to electric heating units, and more particularly to a connection between a heating element and a terminal thereof.

Attempts have been made to provide connec- 5 tions between heating elements and their terminals, which may be cheaply constructed and readily assembled, and at the same time provide a good electrical connection. Such an attempt is illustrated by the patent to Abbott No. 1,494,938. The present invention, which is a continuation in part of my application Serial No. 650,715, now Patent No. 2,049,387, dated July 28, 1936, is an improvement over the above patent and provides a connection which may be made considerably more cheaply than any heretofore known, and provides an electrical connection which is equally as good as any heretofore known. Briefly, the connection is secured by providing a terminal end of the heating element with a helical coil of predetermined diameter and telescoping it over a terminal of predetermined slightly larger diameter, having a surface generated by a straight line.

An object of the invention, therefore, is to provide a connection between a conducting terminal and an electrical heating element wherein the respective parts are maintained against relative disengaging movement by frictional engagement. Another object of the invention is to provide a method for assembling a heating element on a conducting terminal, which comprises expanding a helical conductor over a terminal.

These and other objects will be apparent from the following specification when taken with the accompanying drawing disclosing a sectional view disclosing a preferred embodiment of my invention.

Referring particularly to the drawing, the resistance heating element l is shown in the form of a helical coil supported between two supports 2 which may be any construction in which the heating element is used. Metallic terminals 3 internally threaded are bolted to the supports 2 by the screws 4 threadably passing through them. The screws 4 are passed entirely through the terminals 3 and have received about their ends and support the hollow insulating rod 5 supporting the resistance heating element l.

The terminals 3 are cylindrical and have a pre- 5 determined diameter. The ends of the heating element are in the form of helical coils and of normally slightly less diameter than the terminals 3, and preferably the helicals at the extreme end have a less pitch than those adjacent thereto. According to the present invention the heating element I is assembled on each terminal 3 by rotating the heating element relatively with respect to the respective terminals in a direction tending to untwist it, and at the same time moving the end coils telescopically over the terminals. The result is that the coils are slightly expanded and readily slide on the terminals 3 into assembled position. When the untwisting stress is removed, the coils tend to resume their normal diameter and contract into tight fricw tional engagement with the terminals 3. Preferably the terminals 3 have rounded outer ends 6 to guide the helical coils onto them. The terminals may take other forms, the surfaces of which are generated by a straight line such as of 15 a cone, for instance, without departing from the spirit and scope of the invention.

The holding force can be materially increased by relatively rotating the heating element with respect to the terminals in a twisting or screwing 20 up direction and maintaining it so stressed. When both ends of a helical heating element are connected to terminals according to this invention, itwill be obvious that a twisting up stress in the element will act to simultaneously increase so the holding force at each end. The same result is true in the case of a non-helical heating element as well, due to its torsional resiliency.

The insulating rod 5 is not essential to this invention, acting only as a support for the inter- {In mediate portion of the heating element and also is of slightly less diameter than the terminal 3 so that there will be no interference in the contracting of the coils on the terminals 3.

It will be obvious from the foregoing that the particular supports 2 are not a part of the invention and that the terminals 3 may be supported in any manner desired. Further, the invention is not limited to a resistance heating element helical in form throughout its length or to such an element connected according to this invention at both ends. By this invention I have provided an inexpensive connection which will not work loose during use, one which can be assembled in a minimum length of time, one which pro- 45 vides a perfect electrical contact, and one which may be used wherever a resistance heating element is employed.

What I claim as new and desire to secure by Letters Patent is:

In an electric heater, a helical resistance element, comprising a bare metallic resilient wire in the form of a helical coil of uniform diameter throughout its entire length when unstressed, a cylindrical conducting terminal for said wire,

and means for connecting said wire to said terminal, said means comprising a portion of said helical wire telescopically disposed about said terminal and held thereon solely by its inherent resiliency, the diameter of said terminal being slightly greater than the inner unstressed diameter of said helically coiled wire, the connection between said element and said terminal being characterized by the fact that it is efiected by a slight relative rotation between said parts in a direction tending to unwind said helical element.

WILLARD O. TWOIVLBLY. 

